Scanner control for Lidar systems

ABSTRACT

A scanner and a method for controlling the scanner for a Lidar system are provided. The method comprises: producing a trigger signal by a positional sensor of the scanner; generating a single drive signal comprising a first component at a first frequency and a second component at a second frequency, the first component and the second component are superposed with a fixed phase relationship with aid of the trigger signal; transmitting the single drive signal to the scanner, and the scanner has resonant responses at the first frequency; and actuating the scanner to move in a first periodic motion at the first frequency about a first axis, and move in a second periodic motion at the second frequency about a second axis.

CROSS-REFERENCE

This application is a Continuation Application of International PatentApplication PCT/CN2019/085716, filed May 6, 2019; the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

Lidar (light detection and ranging) technology can be used to obtainthree-dimensional information of an environment by measuring distancesto objects. A Lidar system may include at least a light sourceconfigured to emit a light pulse and at least a detector configured toreceive a returned light pulse. The returned light pulse or light beammay be referred to as echo light beam. Based on the lapse time betweenthe emission of the light pulse and detection of the returned lightpulse (i.e., time of flight), a distance can be obtained. The lightpulse can be generated by a laser emitter then shaped (collimated orfocused) through a lens or lens assembly. The returned light pulse maybe received by a detector located near the laser emitter. The returnedlight pulse may be scattered light from the surface of an object.

In some situations, multiple light pulses or sequence of light pulsesmay be emitted into an environment for scanning across a large area. Insome cases, a Lidar system may utilize a scanner to steer one or morelight beams in one or more directions following a scanning pattern. Itis important to provide an improved scanner control for a Lidar systemthereby improving the efficiency of sampling the environment orproviding adaptive scanning patterns.

SUMMARY OF THE INVENTION

A need exists for improved Lidar system for three-dimensionalmeasurement. A further need exists for a Lidar system with fine grainedcontrollable scanning pattern. In some cases, a Lidar system may utilizea scanner to steer one or more light beams into one or more directionsthat may require the movement of the scanner to be controlled by animproved control system. In some cases, in order to achieve a desiredscanning pattern, movement of the scanner may be controlled at afine-grained level. The provided Lidar system may address the aboveneeds by providing an improved scanner that is configured to directlight pulses following a configurable scanning pattern. In some cases,in order to achieve a desired scanning pattern, systems or methods ofthe present disclosure provide mechanisms for controlling the scannerthereby improving the efficiency of sampling the environment andallowing for automatic adaptation to various real-time conditions. Inparticular, the scanning pattern/path and/or measurement resolution maybe adaptive to real-time conditions (e.g., environment conditions). Theprovided Lidar system may be capable of dynamically adjusting theresolution of sampling points emitted into selected region in 3D space,and the x and/or y resolution of pixels in selected region in a 3D pointcloud image. The provided method and apparatus can be used incombination with light source control such that light beams may beemitted into space in accordance with the movement of the scanner. Byintegrating the control of both the scanner and the light sources, pixel(points) distribution or resolution in selected regions of an imageframe can be dynamically controlled in both x and y directions.Moreover, the provided mechanism may allow for Lidar images or pointcloud images stabilized across image frames.

In one aspect of the invention, a method is provided for controlling ascanner of a Lidar system. The method may comprise: producing a triggersignal by a positional sensor of the scanner; generating a single drivesignal comprising a first component at a first frequency and a secondcomponent at a second frequency, further the first component and thesecond component are superposed with a fixed phase relationship with aidof the trigger signal; transmitting the single drive signal to thescanner, and the scanner has resonant responses at the first frequency;and actuating the scanner to move in a first periodic motion at thefirst frequency about a first axis, and move in a second periodic motionat the second frequency about a second axis.

In some embodiments, the scanner includes a single multi-axis mirror. Insome embodiments, the first periodic motion is at a first resonantfrequency of the scanner about the first axis. In some embodiments, thesecond periodic motion is at a second resonant frequency of the scannerabout the second axis. In some embodiments, the second componentcomprises a ramp waveform. In some cases, the second component comprisesa low frequency waveform component and a high frequency waveformcomponent. In some examples, the high frequency waveform component is ata frequency twice that of the first frequency of the first component andthe high frequency waveform component and the low frequency waveformcomponent are synchronized with aid of the trigger signal.Alternatively, the high frequency waveform component has variableamplitude and the high frequency waveform component and the lowfrequency waveform component are combined with a pre-determined phaserelationship. In some cases, the high frequency waveform component isgenerated in response to real-time conditions. Such real-time conditionsmay include detection of a target.

In some embodiments, the trigger signal is generated at the start or endof a sweep cycle of the first periodic motion. In some embodiments, thesecond component is generated in response to receiving the triggersignal. In some embodiments, the positional sensor is an optic positionsensor or positional sensitive detector.

In some embodiments, the scanner is directing a sequence of light pulsesalong a scanning pattern that approximates a raster scan pattern. Insome cases, the method may further comprise dynamically adjusting thescanning pattern along the second axis direction according to real-timeconditions. For instance, adjusting the scanning pattern along thesecond axis direction comprises varying the second periodic motion bysuperposing a high frequency waveform component to the single drivesignal. In such instance, an amplitude or frequency of the highfrequency waveform component is determined based on the real-timeconditions. In some cases, the method may further comprise dynamicallyadjusting the scanning pattern along the first axis direction accordingto real-time conditions. For instance, adjusting the scanning patternalong the first axis direction comprises varying time intervals ofemitting the sequence of light pulses.

Another aspect of the present disclosure provides scanner for a Lidarsystem. The scanner may comprise: a scanner actuated to move in a firstperiodic motion at a first frequency about a first axis, and move in asecond periodic motion at a second frequency about a second axis; apositional sensor configured to generate a trigger signal; and acontroller configured to generate a single drive signal to actuate thescanner, and the single drive signal comprises a first component at thefirst frequency and a second component at the second frequency, furtherthe first component and the second component are superposed with a fixedphase relationship with aid of the trigger signal.

In some embodiments, the scanner comprises a single multi-axis mirror.In some cases, the single multi-axis mirror comprises a scan platesuspended from a gimbal via one or more torsion arms. For example, theone or more torsion arms are in an H shape.

In some embodiments, the first periodic motion is at a first resonantfrequency of the scanner about the first axis. In some embodiments, thesecond periodic motion is at a second resonant frequency of the scannerabout the second axis. In some embodiments, the second componentcomprises a ramp waveform. In some cases, the second component comprisesa low frequency waveform component and a high frequency waveformcomponent. For instance, the high frequency waveform component is at afrequency twice that of the first frequency of the first component andin some situations, the high frequency waveform component and the lowfrequency waveform component are synchronized with aid of the triggersignal. In some cases, the high frequency waveform component hasvariable amplitude. For instance, the high frequency waveform componentand the low frequency waveform component are combined with a fixed phaserelationship or the high frequency waveform component is generated inresponse to real-time conditions. For example, the real-time conditionsmay include detection of a target.

In some embodiments, the positional sensor is an optic position sensoror positional sensitive detector. In some embodiments, the positionalsensor is for detecting a motion of the scanner. In some embodiments,the trigger signal is generated at the start or end of a sweep cycle ofthe first periodic motion. In some embodiments, the controller isconfigured to generate the second component in response to receiving thetrigger signal. In some embodiments, the scanner is directing a sequenceof light pulses along a scanning pattern that approximates a raster scanpattern. In some cases, the scanning pattern is dynamically adjustedalong the second axis direction according to real-time conditions. Insome situations, the scanning pattern is adjusted by superposing a highfrequency waveform component to the single drive signal to vary thesecond periodic motion. For instance, an amplitude or frequency of thehigh frequency waveform component is determined based on the real-timeconditions. In an example, the real-time conditions include detection ofa target.

In some embodiments, the positional sensor is an optic position sensoror positional sensitive detector. In some embodiments, the positionalsensor is for detecting a motion of the scanner. In some embodiments,the trigger signal is generated at the start or end of a sweep cycle ofthe first periodic motion. In some embodiments, the controller isconfigured to generate the second component in response to receiving thetrigger signal.

In some embodiments, the scanner is directing a sequence of light pulsesalong a scanning pattern that approximates a raster scan pattern. Insome cases, the scanning pattern is dynamically adjusted along thesecond axis direction according to real-time conditions. In some cases,the scanning pattern is adjusted by superposing a high frequencywaveform component to the single drive signal to vary the secondperiodic motion. In some situations, an amplitude or frequency of thehigh frequency waveform component is determined based on the real-timeconditions. In some cases, the scanning pattern is dynamically adjustedalong the first axis direction according to real-time conditions. Insome situations, the scanning pattern is adjusted by varying timeintervals of emitting the sequence of light pulses.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only exemplary embodiments of the presentdisclosure are shown and described, simply by way of illustration of thebest mode contemplated for carrying out the present disclosure. As willbe realized, the present disclosure may be capable of other anddifferent embodiments, and its several details are capable ofmodifications in various obvious respects, all without departing fromthe disclosure. Accordingly, the drawings and description are to beregarded as illustrative in nature, and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 schematically shows an example of a Lidar system, in accordancewith some embodiments of the invention.

FIG. 2 shows an example of a distorted scanning pattern and a rasterscanning pattern.

FIG. 3 schematically shows an example of a multi-axis scanning mirror,in accordance with some embodiments of the invention.

FIG. 4 schematically shows an example of a multi-axis scanning mirror,in accordance with some embodiments of the invention.

FIG. 5 shows an example assembly of a scanning mirror, in accordancewith embodiments of the invention.

FIG. 6 shows an example of a sensor configured to provide signals forsynchronizing or combining drive signal components or individualwaveforms.

FIG. 7 shows examples of waveforms for driving a scanning mirror, inaccordance with some embodiments of the invention.

FIG. 8 shows an example of a waveform for driving a scanning mirror withraster pinch correction, in accordance with some embodiments of theinvention.

FIG. 9 shows another example of composite drive signals exemplified byindividual waveforms, in accordance with some embodiments of theinvention.

FIG. 10 schematically shows an example of varying a drive signalcorresponding to a slow scan motion, in accordance with some embodimentsof the invention.

FIG. 11 shows an example of a scanning pattern with configurabledistribution of pixels.

FIG. 12 schematically shows an example of configuring distributionand/or density of pixels/measurement points dynamically in response toreal-time conditions.

FIG. 13 schematically shows a block diagram of a control system for ascanner, in accordance with some embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

While preferable embodiments of the invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention.

A Lidar system may be referred to as a laser ranging system, a laserradar system, a LIDAR system, or a laser detection and ranging (LADAR orladar) system. Lidar is a type of ranging sensor characterized by longdetection distance, high resolution, and low interference by theenvironment. Lidar has been widely applied in the fields of intelligentrobots, unmanned aerial vehicles, autonomous driving or self-driving.The working principle of Lidar is estimating a distance based on a roundtrip time (e.g., time of flight) of electromagnetic waves between asource and a target.

In some cases, a Lidar system may comprise an emitting apparatus thatemits laser pulses into the environment to scan across a space. Asequence of laser pulses may be emitted following a scanning pattern. Ascanning pattern (which may be referred to as an optical scanningpattern, optical scan path, or scan path) may refer to a pattern or pathalong which a laser beam or laser beam spot is directed. Along thisscanning pattern, a plurality of laser beam spots may or may not beuniformly distributed. The scanning pattern may be controlled by variousfactors such as a movement of a scanner or an arrangement of a pluralityof light sources.

In some embodiments, the scanner may include one or more scanningmirrors that are configured to rotate, oscillate, tilt, pivot, or movein an angular manner about one or more axes. In some cases, the scannermay be a two-dimensional (2D) scanner. The scanner may use a singlescanning mirror that is driven to rotate around both scanning axes. Insome cases, the scanning mirror may be driven to perform a fast scanalong one axis and a slow scan along the other axis. The two axes may beorthogonal to each other. Conventionally, the fast scan sweeps back andforth horizontally across the field of view (FOV) while the slow scansweeps back and forth along with vertical direction across the field ofview. The fast scan operates at a relatively high scan rate while theslow scan operates at a scan rate equal to the video frame rate. In somecases, the fast scan operates resonantly while the slow scan provides asubstantially sawtooth pattern, scanning progressively down the framefor a (large) portion of the frame time and then flying back to the topof the frame to start over or scanning backward from bottom to top in acontinuous fashion. In other cases, interleaved sawtooth scanning,triangular wave scanning, sinusoidal scanning and other waveforms may beused to drive one or both axes. A full sweep along the fast axis may bein any range such as over a ±60° angular range, ±50°, ±40°, ±30°, ±20°,±10° or any value in between. A full sweep along the slow axis may be inany range such as over a ±60° angular range, ±50°, ±40°, ±30°, ±20°,±10° or any value in between.

The single scanning mirror may be controlled to follow a scan path thatsubstantially covers the field of view (FOV). As an example, the scanpath may result in a point cloud with pixels that substantially coverthe FOV. The pixels may be distributed across the FOV according to thescanning pattern. In some cases, by controlling the movement of thescanning mirror, the pixels may have a particular non-uniformdistribution (e.g., the pixels may have a higher density in one or moreselected regions of the FOV). Alternatively or in addition to, bycontrolling the movement of the scanning mirror, the pixels may beevenly distributed along the scanning pattern.

In some cases, a pixel or measurement point may correspond to a lightpulse. In alternative cases, a pixel or measurement point may correspondto multiple light pulses. A pixel or measurement point may be a distancemeasurement point. In some cases, a distance measurement point may begenerated using a single light pulse. In some cases, a measurement pointmay be obtained by emitting a sequence of encoded light pulses emittedwithin short time duration such that the sequence of light pulses may beused to derive a distance measurement point. For example, Lidar can beused for three-dimensional (3D) imaging (e.g., 3D point cloud) ordetecting obstacles. In such cases, a distance measurement associatedwith a sequence of light pulses can be considered as a pixel, and acollection of pixels emitted and captured in succession (i.e., “pointcloud”) can be rendered as an image or analyzed for other reasons (e.g.,detecting obstacles). A sequence of light pulses may be generated andemitted within a duration of, for example, at least 10 ns, 20 ns, 30 ns,40 ns, 50 ns, 60 ns, 70 ns, 80 ns, 90 ns, 100 ns, 200 ns, 300 ns, 400ns, 500 ns, 600 ns, 700 ns, 800 ns, 900 ns, 1 μs, 2 μs, 3 μs, 4 μs, 5μs, 50 μs, 100 μs, 200 μs, 300 μs, 400 μs, 500 μs, or more. In somecases, the time intervals between consecutive sequences may correspondto the temporal resolution of 3D imaging. The temporal resolution of apoint cloud image may also affect the pixel resolution in a horizontaldirection or fast scan direction. The time intervals among sequences maybe constant or variable.

It should be noted that a fast scan direction does not need to bealigned with the horizontal direction (rotating about a vertical scanaxis) and a slow scan direction does not to be aligned with the verticaldirection (rotating about a horizontal scan axis). The fast scandirection and/or slow scan direction can be in any orientation withrespect to the ground reference frame.

As utilized herein, terms “sequence of light pulses”, “sequence ofpulses”, “sequence of signals” and the like are used interchangeablythroughout the specification unless context suggests otherwise. Terms“measurement signals”, “measurement pulses”, “signal lights”, “outputbeams” and the like may refer to light pulses emitted from the emittingapparatus of the Lidar system unless context suggests otherwise. Terms“echo beams”, “return signals”, “return pulses” and the like may referto light pulses received by the detector of the Lidar system and areused interchangeably throughout the specification unless contextsuggests otherwise.

The output beam or signal light may then be directed into a space formeasurements. As an example, output beam may have an average power ofapproximately 1 mW, 10 mW, 100 mW, 1 W, 10 W, or any other suitableaverage power. As another example, output beam may include pulses with apulse energy of approximately 0.1μ. 1, 1μ. 1, 10μ. 1, 100μ. 1, 1 mJ, orany other suitable pulse energy. As another example, output beam mayinclude pulses with a peak power of approximately 10 W, 100 W, 1 kW, 2kW, 5 kW, 10 kW, or any other suitable peak power. An optical pulse witha duration of 400 ps and a pulse energy of 1μ, has a peak power ofapproximately 2.5 kW. If the pulse repetition frequency is 500 kHz, thenthe average power of an output beam with 1 μJ pulses is approximately0.5 W. In some cases, the wavelength of the output beam may be in therange of 900 nm to 1600 nm or in any other suitable range. In somecases, the wavelength of the output beam may be in the range of 1530 nmto 1570 nm to provide eye-safe laser.

FIG. 1 schematically shows an example of a Lidar system 100. In someembodiments, a Lidar system 100 may comprise an emitting module 110, areceiving module, a scanner 120, and a plurality of optical componentssuch as lens assembly 161, 165, mirror 163.

The emitting module 110 may comprise at least one light sourceconfigured to generate laser beams or pulses of light. The wavelength ofthe laser beam may be in any suitable range depending on the specificapplication. In some cases, the light source may include eye-safe laser.An eye-safe laser may refer to a laser with an emission wavelength,average power, peak power, peak intensity, pulse energy, beam size, beamdivergence, or exposure time such that emitted light from the laserpresents little or no possibility of causing damage to a person's eyes.As an example, light source may be classified as a Class 1 laser product(as specified by the 60825-1 standard of the InternationalElectrotechnical Commission (IEC)) or a Class I laser product (asspecified by Title 21, Section 1040.10 of the United States Code ofFederal Regulations (CFR)) that is safe under all conditions of normaluse. In some embodiments, the light source may include an eye-safe laser(e.g., a Class 1 or a Class I laser) configured to operate at anysuitable wavelength between approximately 1400 nm and approximately 2100nm. In some cases, a light source may include an eye-safe laser with anoperating wavelength between approximately 1400 nm and approximately1600 nm. In some cases, a light source may include an eye-safe laserwith an operating wavelength between approximately 1530 nm andapproximately 1560 nm.

The light source may include a laser diode. The light source may includeany suitable type of lasers, such as for example, a Fabry-Perot laserdiode, a quantum well laser, a distributed Bragg reflector (DBR) laser,a distributed feedback (DFB) laser, or a vertical-cavitysurface-emitting laser (VCSEL). In some cases, the light source mayinclude a fiber-laser module. In an example, the fiber-laser module mayinclude a current-modulated laser diode with a peak wavelength ofapproximately 1550 nm followed by a single-stage or a multi-stageerbium-doped fiber amplifier (EDFA). The fiber-laser module may includea seed laser, a pump laser, an optical amplifier (e.g., gain fiber orfiber amplifier) and other components.

The output beam or signal light may be directed to one or more opticalelements (e.g., reflectors) and/or pass through a lens assembly 161(e.g., collimation lens, collimation lens assembly) for collimating orfocusing light beams 111. The Lidar system 100 can include any suitableoptical components such as one or more lenses, mirrors, filters (e.g.,bandpass or interference filters), beam splitters, polarizers,polarizing beam splitters, wave plates (e.g., half-wave or quarter-waveplates), diffractive elements, or holographic elements, telescope, toexpand, focus, or collimate the output beam 111 to a desired beamdiameter or divergence.

Similarly, the returned light beams 131 may pass through one or moreoptical components 165 so that the returned light beams can be directed,focused onto an active region of a detector of the detecting module 130.The one or more optical components can include, for example, one or moremirrors (e.g., flat mirror, concave mirror, convex mirror, parabolicmirror) or lens/lens assembly to direct the returned light beams to thedetector.

The Lidar system 100 may comprise a mirror 163 configured to allowsignal light 111 pass through the mirror meanwhile direct the returnedlight 131 to the detector. In some cases, the mirror 163 may include ahole, slot, or aperture which allows the signal light 111 pass through.In some cases, the mirror 163 may be configured so that at least afraction (e.g., at least 90%, 80%, 70%, 60%, etc) of the signal light111 passes through mirror and at least a fraction (e.g., at least 90%,80%, 70%, 60%, etc) of the returned light beams 131 is reflected bymirror 163. In some cases, the mirror 163 may provide for signal light111 and returned light beam 131 to be substantially coaxial so that thetwo beams travel along substantially the same optical path but inopposite directions. For example, the mirror 163 may include a hole,slot, or aperture which the signal light 111 passes through and areflecting surface that reflects at least a portion of the returnedlight beam 131 toward an active region of the detector 130.

The detecting module 130 may comprise one or more detectors configuredto receive the echo beams 160. A detector may be a photoreceiver,optical receiver, optical sensor, photodetector, or optical detector. Insome cases, a detecting module may include one or more avalanchephotodiodes (APDs) or one or more single-photon avalanche diodes(SPADs). In some cases, a receiving module may include one or more PNphotodiodes (e.g., a photodiode structure formed by a p-typesemiconductor and an n-type semiconductor) or one or more PINphotodiodes (e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions).

The returned light beam may be directed to an active region of thedetector. The active region may have any suitable size or diameter, suchas for example, a diameter of approximately 25 μm, 50 μm, 80 μm, 100 μm,200 μm, 500 μm, 1 mm, 2 mm, or 5 mm. In some cases, the mirror 163 mayhave a reflecting surface that is substantially flat or the reflectingsurface may be curved (e.g., mirror may be an off-axis parabolic mirrorconfigured to focus the input beam 131 onto an active region of thereceiver). A reflecting surface of the mirror 163 may include areflective metallic coating (e.g., gold, silver, or aluminum) or areflective dielectric coating, and the reflecting surface may have anysuitable reflectivity R at an operating wavelength of the light source(e.g., R greater than or equal to 70%, 80%, 90%, 95%, 98%, or 99%).

In some embodiments, the Lidar system 100 may comprise an opticalreceiving device 165 (e.g., focusing lens, focusing lens assembly), oneor more optical elements (e.g., reflectors) 163 that allow for thereflected light off an external object pass through the opticalreceiving device and then is received by the detecting module 130. Thereceived optical signals may be converted to electrical signals andprocessed by the controller 140.

The Lidar system 100 may include a scanner 120 to steer the output beam111 in one or more directions. The scanner 120 may be configured to scanthe output beam 111 over an angular range. In some cases, the scanner120 may be configured to scan the output beam 111 over a 5-degreeangular range, 20-degree angular range, 30-degree angular range,60-degree angular range, or any other suitable angular range. As anexample, a scanning mirror may be configured to periodically oscillateor rotate back and forth over a 15-degree range, which results in theoutput beam 111 scanning across a 30-degree range (e.g., a Θ-degreerotation by a scanning mirror results in a 20-degree angular scan ofoutput beam). In some embodiments, a field of regard (FOR) of a Lidarsystem 100 may refer to an area, region, or angular range over which theLidar system may be configured to scan or capture distance information.As an example, a Lidar system with an output beam 111 with a 30-degreescanning range may be referred to as having a 30-degree angular field ofregard. As another example, a Lidar system 100 with a scanning mirrorthat rotates over a 30-degree range may produce an output beam 111 thatscans across a 60-degree range (e.g., a 60-degree FOR). In particularembodiments, Lidar system 100 may have a FOR of approximately 10°, 20°,40°, 60°, 120°, or any other suitable FOR. In some cases, a FOR may bereferred to as a full scan region.

In some embodiments, the scanner 120 may include one or more scanningmirrors that are configured to rotate, oscillate, tilt, pivot, or movein an angular manner about one or more axes. In some cases, a flatscanning mirror 125 may be attached to a scanner actuator or mechanismwhich actuates the mirror to scan over a particular angular range. Insome cases, the scanner 120 may include a resonant scanning mirror oroscillation mirror 125. In some cases, the scanner may be atwo-dimensional (2D) scanner. The scanner may use a single scanningmirror that is driven to rotate around both scanning axes. In somecases, the scanning mirror may be driven to perform a fast scan alongone axis and a slow scan along the other axis. The two axes may beorthogonal to each other. The scanning mirror 125 may be designed suchthat single scanning mirror has resonant responses at one or morefrequencies of the drive signal to produce a desired periodic movement.For example, the resonant frequency and amplification factor of thescanning mirror may be selected independently in each of two axes bydistributing its mass differently about each of the axes and bydesigning the supporting structures (e.g., support arms or torsional armthat have different torsional stiffness in each axis). Details about thedesign of the scanning mirror and drive signals are described laterherein.

The scanner can be actuated by any suitable actuator or mechanism suchas galvanometer scanner, a piezoelectric actuator, a polygonal scanner,a rotating-prism scanner, a voice coil motor, an electric motor (e.g., aDC motor, a brushless DC motor, a synchronous electric motor, or astepper motor), or a microelectromechanical systems (MEMS) device andthe like.

A resonant scanner (which may be referred to as a resonant actuator) mayinclude a spring-like mechanism driven by an actuator to produce aperiodic oscillation at a substantially fixed frequency. The periodicoscillation frequency associated with the fast scanning axis may be thesame as the resonant frequency about the fast scanning axis. Theperiodic oscillation frequency at which the scanning mirror is rotatedabout the slow scanning axis may be the resonant frequency about theslow scanning axis or an off resonance frequency component. Theoscillation frequency about the fast scanning axis may be about 1 kHz.The fast scanning oscillation frequency can be any value below 1 kHz orabove 1 kHz. The slow scanning oscillation frequency can be any value inthe range of about 10 Hz to 100 Hz. The slow scanning oscillationfrequency can be any value below 10 Hz or above 100 Hz. In some cases,the fast scanning oscillation frequency and the slow scanningoscillation frequency may have a pre-determined relationship. Forexample, the fast scanning oscillation frequency can be at least about4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40,50, 60, 70, 80, 90, or 100 times of slow scanning oscillation frequency.

The scanner 120 may include a scanning mirror 125 that can have anysuitable geometry or dimension such that the scanning mirror mayoscillate at a resonant frequency about one or more axes in response toa drive signal. In some cases, the scanning mirror may include a scanplate having a diameter or width between approximately 3 mm and 15 mm.In some cases, the scanning mirror may also receive returned light beams131 and direct the returned light beams to the mirror 163.

The scanning mirror can be rotated by any suitable actuation mechanismsuch as rotated using electromagnetic actuation. In an example, ascanning mirror may be actuated by a voice coil motor (which may bereferred to as a voice coil actuator) which may include a magnet andcoil. When an electrical current is supplied to the coil, atranslational force is applied to the magnet, which causes the scanningmirror attached to the magnet to move or rotate. A galvanometer scanner(which may be referred to as a galvanometer actuator) may include agalvanometer-based scanning motor with a magnet and coil. When anelectrical current is supplied to the coil, a rotational force isapplied to the magnet, which causes a mirror attached to thegalvanometer scanner to rotate. The electrical current supplied to thecoil may be controlled to dynamically change the position of thegalvanometer mirror.

In some embodiments, the scanner 120 may include a scanner control unit121 which may control the scanning mirror(s) so as to guide the outputbeam 111 in a desired direction or along a desired scanning pattern. Thescanner control unit 121 may generate a drive signal to actuate thescanning mirror 125. The drive signal to actuate the scanning mirror maycomprise one or more components having different frequencies or one ormore individual waveforms. In some cases, the drive signal may be asingle drive signal comprising multiple frequency components (e.g.,multiplexed frequencies) such that at least one of the frequencycomponents is modulated at the resonant frequency of the fast scan andat least one of the frequency components is for the slow scan. Thefrequency for the slow scan may or may not be the resonant frequencyabout the slow scan axis. The signal component for the slow scan can bea superimposed waveform comprising different frequency components.Alternatively, separate drive signals corresponding to the two scanningaxes may be supplied to the scanning mirror. Details about the drivesignals and waveform (frequency) components are described later herein.

In some cases, the scanner 120 may further include one or more sensors123 configured to detect the angle position and/or angular motion of thescanning mirror. The positional signal 150 may be transmitted to thescanner control unit 121 for controlling the driving signal of thescanner. In some embodiments, the positional signal 150 may be used tosynchronize the oscillation in the two axes thereby stabilizing thepoint cloud images from frame to frame. For instance, with aid of thepositional signal, the zero speed position of a horizontal oscillationcycle is synchronous with the start or end of the vertical oscillationcycle so that the coordinates of pixels (points) across different framesare substantially the same.

Any suitable sensors can be used to detect the motion or angularposition of the scanning mirror. For example, piezo-resistive,photodetector, optical position sensor (OPS), position sensitivedetector (PSD) or other sensors can be used to sense the motion orposition. In some cases, a PSD may be used to measure the angularposition of the scanning mirror. The angular position may be measuredwith an angular resolution of no more than 0.01 degree, 0.05 degree, 0.1degree, or any value below 0.01 degree or above 0.1 degree.

In optional embodiments, the positional signal 150 or a sensor signalgenerated by the position sensor 123 may also be used by the emittingmodule 110 to coordinate light pulses and the motion of the scanningmirror. This may beneficially allow for adjusting the distribution orresolution of pixels (measurement points) in selected regions both thefast scan and slow scan directions.

In the case when a 2D resonant scanner is utilized, the scan speed of aresonant scanner is constantly changing in both horizontal and verticaldirections. Like a pendulum, the scanner may be accelerating toward thecenter and then decelerating toward the end of the sweep. Then itreverses the cycle. This may result in a non-straight horizontal line(i.e., fast scanning lines) and/or undesired pixels distribution in thescanning pattern. FIG. 2 shows an example of a scanning pattern 201suffer from raster pinch distortion and a raster scanning pattern 203with the distortion corrected. The scan pattern 201 without the rasterpinch correction may be “pinched” at the outer edges of the field ofview in the horizontal direction. That is, in successive forward andreverse sweeps of the light pulses, the pixels near the edge of the scanpattern are unevenly spaced. This uneven spacing can cause the pixels tooverlap or can leave a gap between adjacent rows of pixels. Thedistribution of the rows of horizontal lines is also uneven in thevertical direction resulting in sparse pixels towards the center of thefield of view and denser pixels towards the top and bottom of the fieldof view.

The provided scanner or Lidar system may provide improved scannercontrol so that the measurements points along the scanning pattern canbe stabilized across image frames, the scanning pattern may betterapproximate a raster pattern with a built-in raster pinch correctionfeature, and/or distribution (resolution) of pixels along the slow scandirections (i.e., cycles of fast scan along slow scanning direction) canbe configured and controlled in substantially real-time. As will bedescribed later herein, the scan path followed by the light pulses inresponse to a ramped vertical scan (exemplified by individual waveformsincluding a low frequency component and a high frequency component twicethat of the fast scan) may approximate a raster scan pattern.

In some embodiments of the invention, a single scanning mirror may beutilized to perform oscillation movement about two or more axes. Thescanning mirror may be a resonant mirror with geometrics, massdistribution and structures designed such that the scanning mirror mayoscillate at a resonant frequency about one or more axes in response toa drive signal. The two axes may correspond to a fast scan axis and aslow scan axis.

FIG. 3 schematically shows an example of a multi-axis scanning mirror300, in accordance with some embodiments of the invention. The scanningmirror 300 may be actuated to rotate about a fast scan axis 301 and aslow scan axis 303. In the illustrated example, movement about the fastscan axis 301 may result in horizontal scan cycles and movement aboutthe slow scan axis 303 may result in periodic vertical scan.

In some embodiments, the scanning mirror 300 may include a scan plate317. The scan plate 317 may include a mirror formed thereon or attachedthereto. The scan plate 317 may have a diameter or width betweenapproximately 3 mm and 15 mm. The scan plate 317 can have any formfactor such as circular, oval, rectangular, square and various others.The movement of the scan plate 317 may be controlled by the system fordirecting the incident light pulses into desired directions such asfollowing a scan pattern.

The scanning mirror 300 may be coupled to actuators or mountingstructures via torsion arms 315. For example, the torsion arms 315 maybe mechanically connected to a fixed substrate or mounting structure forreceiving drive signals. The torsion arms 315 may be coupled to a gimbalframe 316. The gimbal frame 316 can be in any form factor such ascircular, rectangular, oval and the like.

For a given drive frequency, the amplitude of movement of gimbal frame316 (and other structures suspended therefrom) may be proportional tothe voltage of the drive signal and to the mechanical amplificationfactor of the rotating mass at the drive frequency (although notnecessarily linearly proportional). For drive frequency components at ornear the resonance frequency of the gimbal frame (and suspendedstructures), the rotational movement about the slow axis 303 may beamplified. For off resonance drive frequency components, the amplitudeof rotation of the gimbal frame is reduced and, at certain frequencyranges, inverted. In some cases, frequency of the drive signal may beselected to not be at the resonant frequency of the slow axis so as toavoid frequency drift during operation. In alternative cases, resonancefrequency drive component may be used to drive the oscillation responseabout the slow scan axis.

An inner gimbal ring 318 may be suspended from the gimbal frame 316 viatorsion arms 311 allowing the inner gimbal ring and components carriedthereon to rotate about the fast scan axis 301 relative to the gimbalframe 316. The combined mass and distribution of mass of the assemblycomprising the scan plate 317, the inner gimbal ring 318, and thestiffness of torsion arms 311 may determine a resonant frequency andamplification factor for the rotation of scan plate 317 about the fastscan axis 301. Any suitable resonant frequency and amplification factorfor the fast scan axis or both of the two axes can be selected byvarying the mass distribution and mass of the components and/orstiffness of the torsion arms. The oscillation frequency about the fastscanning axis may be the resonant frequency which can be about 1 kHz.The fast scanning oscillation frequency can be any value below 1 kHz orabove 1 kHz. The slow scanning oscillation frequency can be any value inthe range of about 10 Hz to 100 Hz. The slow scanning oscillationfrequency can be any value below 10 Hz or above 100 Hz. In some cases,the fast scanning oscillation frequency and the slow scanningoscillation frequency may have a pre-determined relationship. Forexample, the fast scanning oscillation frequency can be at least about4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40,50, 60, 70, 80, 90, or 100 times of slow scanning oscillation frequency.

In some embodiments, the scan plate 317 may be coupled to an innergimbal ring 318 via torsion arms 313. The torsion arms may be coupled totwo opposing sides of the scan plate 317. As can be seen, the scan plate317 is suspended from the inner gimbal ring 318 by torsion arms 313 suchthat the scan plate 317 is allowed to rotate about the slow scan axis303 relative to the inner gimbal ring 318. Introducing the torsion arms313 and inner gimbal ring 318 may allow the scan plate 317 to have asecondary mode that is twice of the resonant frequency of the fast scanaxis such that the raster pinch distortion can be corrected. Forexample, in order to correct the raster pinch distortion, the drivesignal may be a single composite drive signal that contains thesuperposition of vertical drive waveform at a slow frequency (e.g.,resonant frequency of the slow scan axis) and a vertical drive sawtoothwaveform at twice of the resonant frequency of the fast scan axis, theinner gimbal ring 318 may oscillate with a resonant frequency in mode 2owning to the torsion arms and the inner gimbal ring.

The scanning mirror 300 may comprise or be actuated by an actuator(e.g., coil). The actuator may be driven to produce rotational movementof the gimbal frame 316, the inner gimbal ring 318 and suspended scanplate 317 about axes 301, 303. In some cases, a combined coil may beincluded to drive the movement of the scanning mirror about the twoaxes. Alternatively or in addition to, separate coils may be driven toproduce rotational movement of the scan plate 317 about the fast scanaxis, and rotational movement of the assembly comprising the gimbalframe, the inner gimbal ring and scan plate to rotate about the slowscan axis respectively. When the coil receives a signal that isperiodically driven at a rate corresponding to the resonance frequency(or any frequency that produces a suitable response) of the scan plate317 about the fast scan axis, the amplitude of the rotation of scanplate about the fast scan axis can be enhanced owing to the mechanicalamplification factor. In a similar manner, when the coil receives asignal that is periodically driven at a rate corresponding to theresonance frequency of the assembly comprising scan plate, torsion arms,inner gimbal ring and gimbal frame; the assembly may oscillate about theslow scan axis with enhanced amplitude owing to the mechanicalamplification factor thereby achieving a greater angle range withrelative small amount of input energy. Alternatively, the oscillationfrequency associated with the slow scan axis may not be at or near theresonant frequency so as to avoid frequency drift during operation.

FIG. 4 schematically shows another example of multi-axis scanning mirror400, in accordance with some embodiments of the invention. Similar tothe scanning mirror described with respect to FIG. 3, the scanningmirror 400 may be actuated to rotate about a fast scan axis 401 and aslow scan axis 403. In the illustrated example, periodic movement aboutthe fast scan axis 401 may result in horizontal scan cycles and periodicmovement about the slow scan axis 403 may result in periodic verticalscans. The scanning mirror 400 may have different structures forproviding the high frequency response about the slow scan axis allowingfor an overall compact design of the scanning mirror or an increasedeffective/active region of the scan plate.

The scanning mirror 400 may be coupled to actuators or mountingstructures via torsion arms 415 in a similar manner as described in FIG.3. For example, the torsion arms 415 may be mechanically connected to afixed substrate or mounting structure for receiving drive signals. Thetorsion arms 415 may be coupled to a gimbal frame 416 functioning as asupport structure for the scan plate. The gimbal frame 416 can be in anyform factor such as circular, rectangular, oval, square and the like.

For a given drive frequency, the amplitude of movement of gimbal frame416 (and other structures suspended therefrom) may be proportional tothe voltage of the drive signal and to the mechanical amplificationfactor of the rotating mass at the drive frequency (although notnecessarily linearly proportional). For drive frequency components at ornear the resonance frequency of the gimbal frame (and suspendedstructures), the rotational movement about the slow axis 403 may beamplified. For off resonance drive frequency components, the amplitudeof rotation of the gimbal frame is reduced and, at certain frequencyranges, inverted. In some cases, frequency of the drive signal may beselected to an off resonance frequency of the slow scan axis so as toavoid frequency drift during operation. In alternative cases, resonantfrequency may be used to drive the movement about the slow scan axis toachieve a greater angle range. For example, the combined mass anddistribution of mass of the assembly comprising the scan plate 417, anycomponents disposed between the scan plate and the torsion arms 415, andthe stiffness of torsion arms 415 may determine a resonant frequency andamplification factor for the rotation of scan plate 417 about the slowscan axis 403.

The scan plate 417 may be suspended from the gimbal frame 416 via afirst pair of torsion arms 413 a, 413 b, a second pair of torsion arms411 a, 411 b, allowing the scan plate 417 to rotate about the fast scanaxis 401 and slow scan axis 403 relative to the gimbal frame 416. In theillustrated example, the scan plate 417 may be coupled to the gimbalframe 416 via an H-shaped structure disposed on opposing sides of thescan plate 417. Similar to the example described in FIG. 3, introducingthe torsion arms 413 a, 413 b, may allow the scan plate 417 to have asecondary mode that is twice of the resonant frequency of the fast scanaxis such that the raster pinch distortion can be corrected. Asillustrated in the side view 420, a vibration response at resonantfrequency in mode 2 about the slow scan axis can be achieved. Byreplacing the inner gimbal ring and torsion arms with the H-shapedtorsion arms, a compact design or a scan plate with increased effectivearea may be provided at little cost of the overall size of the scanningmirror.

The combined mass and distribution of mass of the assembly comprisingthe scan plate 417, the torsion arms 413 a, 413 b, and the stiffness oftorsion arms 411 a, 411 b may determine a resonant frequency andamplification factor for the rotation of scan plate 417 about fast scanaxis 401. Any suitable resonant frequency and amplification factor forthe fast scanning axis or both of the axes can be selected by varyingthe mass distribution and mass of the components. The oscillationfrequency about the fast scanning axis may be the resonant frequencywhich, in some cases, may be about 1 kHz. The fast scanning oscillationfrequency can be any value below 1 kHz or above 1 kHz. The slow scanningoscillation frequency can be any value in the range of about 10 Hz to100 Hz. The slow scanning oscillation frequency can be any value below10 Hz or above 100 Hz. In some cases, the fast scanning oscillationfrequency and the slow scanning oscillation frequency may have apre-determined relationship. For example, the fast scanning oscillationfrequency can be at least about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, or 100 times of slowscanning oscillation frequency.

The scanning mirror 400 may comprise or be actuated by an actuator(e.g., coil). The actuator may be driven to produce rotational movementof the gimbal frame 416, the H-shaped torsion structures and suspendedscan plate 417 about axes 401, 403. In some cases, a combined coil maybe utilized to drive the movement about the two axes. Alternatively orin addition to, separate coils may be driven to produce rotationalmovement of the scan plate 417 about the fast scan axis, and rotationalmovement of the assembly comprising the gimbal frame, H-shaped torsionstructure and scan plate to rotate about the slow scan axis,respectively. When the coil receives a signal that is periodicallydriven at a rate corresponding to the resonance frequency (or anyfrequency that produces a suitable response) of the scan plate 417 aboutthe fast scan axis, the amplitude of the rotation of scan plate aboutthe fast scan axis can be enhanced owing to the mechanical amplificationfactor. In a similar manner, when the coil receives a signal that isperiodically driven at a rate corresponding to the resonance frequencyof the assembly comprising scan plate, torsion arms, gimbal frame andany components carried thereon; the assembly may oscillate about theslow scan axis with enhanced amplitude owing to the mechanicalamplification factor thereby achieving an increased angle range withrelatively small amount of input energy. Alternatively, the oscillationfrequency associated with the slow scan axis may not be at or near theresonant frequency so as to avoid frequency drift during operation.

FIG. 5 shows an example assembly of a scanning mirror, in accordancewith embodiments of the invention. The scanning mirror 500 can be thesame scanning mirror as described above. For example, the scanningmirror 500 may comprise a scan plate 505 which is coupled to a gimbalframe 501 via torsion arms 503. The scanning mirror may be attached toor fixed to a substrate or mounting unit via torsion arms as describedelsewhere herein. In some cases, the scanning mirror, actuator (notshown) and mounting structures may be enclosed in a case 507, 508. Thecase may have at least a surface 507 having an opening or aperture suchthat light pulses may incident on the scanning mirror 500 and bedirected to one or more directions.

As mentioned above, in order to correct the raster pinch distortionand/or to stabilize the image frames, the drive signal for the slow scanaxis and fast scan axis may be synchronized so that there is asubstantially fixed phase difference between their oscillations. In somecases, the oscillation frequency of the fast scan may be n times of theoscillation frequency of the slow scan where n can be in integer such as2, 3, 4, 5, 6, 7, 8, 10, 15, 20, 25, 30, 25, 40, 45, 50, 60, 70, 80, 90,100 or more. In some cases, the oscillation movements about the two axesmay be synchronous and the phase difference may be zero.

In some embodiments, the synchronization may be achieved with aid of asensor (e.g., positional sensor 123 in FIG. 1). The sensor can be thepositional sensor for controlling the movement of the scanning mirror.Positional signal produced by the positional sensor may be used by thescanner control unit for generating a driving signal of the scanner. Forexample, scanning movement of the scan plate may be detected by thepositional sensor and used for synchronizing or combining multiplecomponents of the drive signals. The positional signal may be generatedwhen the scan plate reaches the ends of a sweep (e.g., start or end). Insome cases, when the scan plate reaches the start or end of a horizontalsweep, the positional signal may be generated and used to trigger acycle of the vertical scan thereby synchronizing the oscillationmovement along the two scan axes. The position signal may be generatedat the start or end of a horizontal (i.e., fast scan) sweep cycle. Insome embodiments, the positional signal may be generated by the sameposition sensor (e.g., sensor 123) as described in FIG. 1.Alternatively, the positional signal can be generated by any othersensor that is capable of detecting the angular position of the scanner.

FIG. 6 shows an example of a sensor 610 configured to provide signalsfor synchronizing or combining drive signal components or individualwaveforms. For example, the sensor signals may be used as trigger signalto synchronize a periodic slow scanning motion with a periodic fastscanning motion. As described above, the sensor 610 may be used todetect the angle position and/or angular motion of a scanning mirror620. The scanning mirror 620 may be configured to rotate, tilt, pivot,or move in an angular manner about one or more axes. The scanning mirror620 can be the same as the scan plate as described elsewhere herein. Anysuitable sensors (e.g., position sensitive detector) can be used todetect the motion or angular position of the mirror. For example,piezo-resistive, photodetector, optical position sensor (OPS) or othersensors can be used to sense the motion or angle position. In someembodiments, the position sensor may be a positional sensitive detector(PSD).

In some situations, the positional signal can also be used by theemitting module to control the light source. For example, the positionalsignals may be used by the emitting module to coordinate light pulsesand the motion of the scanning mirror. This provides advantages ofproviding a triggering signal utilized by both the light sourcecontroller and scanner controller without introducing additionalcomponents to the Lidar system.

In the illustrated example, the position sensor 610 may be located to aside 621 of the scanning mirror that is opposite of the side 623 wherethe output light beams 111 incident on the scanning mirror 620. Theposition sensor 610 may be an optical position sensor that may not be indirect contact with the scanning mirror 620. In the illustrated example,the position sensor 610 may comprise a light source 612 configured forgenerating measurement light. The measurement light may incident on theside 621 of the scanning mirror 620, directed back to the positionalsensor 610 and captured by the detector component 618. The measurementlight can be pulse light or continuous light. In some cases, the side621 of the scanning mirror that is facing the position sensor 610 mayhave a reflective surface such that the measurement light can bedirected back to the position sensor.

The light source 612 and the detector component 618 may be arranged withan angle such that measurement light emitted by the light source can becaptured by an active region of the detector component 618. In somecases, supporting elements 615, 616, 617 may be used to position thelight source and the detector component into a pre-determined angle withrespect to each other and/or with respect to the scanning mirror 620.The light source 612 and/or the detector component 618 may bepermanently fixed to such supporting elements or removably coupled tosuch supporting elements.

The light source 612 can be any suitable light source for generatingmeasurement light. For example, the light source may include laser suchas solid-state laser, gas laser, liquid laser, semiconductor laser,fiber laser, and the like. The detector component 618 may be a positionsensitive detector that can measure a position of a light spot in one ortwo-dimensions on the sensor surface. Based on the position of the lightspot, the angle of the scanning mirror can be calculated. The angularposition may be measured with an angular resolution of no more than 0.01degree, 0.05 degree, 0.1 degree, or any value below 0.01 degree or above0.1 degree.

In some cases, the position sensor 610 may include other components suchas optical filter 614 or connecting board 619 to enhance the measurementsignal or provide electrical connectivity and various otherfunctionalities.

As described above, the fast scan may operate at a relatively high scanrate while the slow scan operates at a scan rate equal to the videoframe rate. In some applications, the fast scan operates resonantlywhile the slow scan provides a substantially sawtooth pattern, scanningprogressively down the frame for a (large) portion of the frame time andthen flying back to the top of the frame to start over or scanningbackward from bottom to top in a continuous fashion. In otherapplications, interleaved sawtooth scanning, triangular wave scanning,sinusoidal scanning and other waveforms may be used to drive one or bothaxes. The drive signal may be a composite signal comprising multiplecomponents or individual waveforms.

One or more components of the drive signal can be synchronized by aclock signal or combined with a fixed phase relationship with aid of theclock signal. FIG. 7 shows examples of waveforms for driving a scanningmirror. As shown in the example 700, the drive signals for producing therotational movements about the fast scan axis and slow scan axis may besynchronized by clock signals 720. The clock signals 720 can be at thesame frequency of the fast scan as described above or at apre-determined times n (n=2, 3, 4, 5, 6, 7, 8, 9, 10, etc) of the fastscan frequency. The clock signal can be pulsed signals, digital signals,continuous signals or any other form. As shown in the example 700, theslow scan waveform 701 may start in response to a clock signal 720 whichis produced when the fast scan sweep reaches a start/end.

In some cases, drive signals for actuating many of the embodimentsaccording to the invention may involve combinations of waveforms. Forexample, waveform 703 is a high frequency signal/component for driving afirst oscillation movement about a first axis at a corresponding highresonant frequency. The waveform 703 in this case may be the drivefrequency component for the fast scan. Waveform 701 is a lower frequencysignal for driving a second oscillation movement about a second axis ata corresponding lower (resonant) frequency. The waveform 701 in thiscase may be the drive frequency component for the slow scan. The slowscan waveform 701 and the fast scan waveform 703 may be compositefrequency components of the drive signals supplied to the scanningmirror.

In some cases, distribution of pixels along the vertical direction(vertical resolution) or slow scan direction may be controlled byvarying the drive signals for the slow scan motion. As shown in theexample 710, a waveform 710 for driving an oscillation movement aboutthe slow scan axis may be a composite signal 711 comprising a lowfrequency component 713 and a high frequency component 715. The twocomponents may be combined with a pre-determined phase relationship suchthat the superimposed signal 711 may drive the scan plate to rotate withincreased/reduced speed in selected time intervals (within a verticalscan cycle) thereby reducing/increasing pixel densities in the selectedregions. The two components may be synchronized or combined with a fixedphase relationship with aid of the clock signal 720.

FIG. 8 shows an example of waveform 801 for driving a scanning mirrorwith raster pinch correction. The waveform for actuating the slow scanmotion may be a ramped waveform. A path followed by the scanned beam orseries of light pulses in response to a ramped vertical scan mayapproximate a raster pattern. The waveform for driving an oscillationmovement about the slow scan axis may be a composite signal 801comprising a low frequency component 803 and a high frequency component805. The low frequency component 803 may be resonant signals which issuperimposed with an off resonance frequency signal such as anapproximately sawtooth waveform 805. The low frequency component 803 mayor may not be at or near the resonant frequency about the slow scanaxis. In some cases, the low frequency component may be at the resonantfrequency in order to achieve a greater range of deflection angle.Alternatively, the low frequency component may be off resonant frequencyso as to avoid frequency drift during operation. The high frequencycomponent 805 may approximate a sawtooth waveform and may be twice ofthe resonant frequency of the fast scan axis. The high frequencycomponent 805 may be useful for driving the scan plate to rotate at theresonant frequency twice that of the fast scan with the phasesynchronized by the clock signal. By combining a high frequencycomponent that twice of the fast scanning motion with a low frequencycomponent and synchronizing them with aid of the clock signal, thescanning mirror may deflect light pulses comprising substantiallyparallel paths in both left-to-right and right-to-left scanningdirections, substantially eliminating raster pinch distortion.

FIG. 9 shows another example of a composite drive signal 901 exemplifiedby individual waveforms 903, 905. As shown in the example, a waveformfor driving an oscillation movement about the slow scan axis may be acomposite signal 901 comprising a low frequency component 903 and a highfrequency component 905. The two components may be combined with apre-determined phase relationship such that the superimposed signal 901may drive the scan plate to move with increased/reduced speed inselected time intervals (within a vertical sweep) therebyreducing/increasing pixel densities in the selected regions. In somecases, the high frequency component may have varied amplitude such thatthe waveform/amplitude of the combined signal can be adjusted at afine-grained controlled level. It should be noted that the highfrequency component 905 may have any arbitrary waveform as long as theresultant composite signal 901 can have desired waveform for slowing oraccelerating the speed in the vertical direction.

FIG. 10 schematically shows an example of varying the drive signalcorresponding to the slow scan motion. Pixels distribution/density alongthe vertical direction as shown in the scanning pattern 1001 is adjustedin response to the drive signal (e.g., drive signal 901 in FIG. 9) sothat vertical resolution is increased in the middle region 1005. Thisalso means that denser measurement pulses are emitted to the middleregion 1005 of the field of view. This beneficially allows for animproved efficiency of sampling the environment.

It should be noted that the drive signals as described above can becombined in any suitable manner to produce a desired effect. Forexample, raster pinch correction and pixel distribution variation can beperformed simultaneously by combining signal components as describedabove. FIG. 11 shows an example of a scanning pattern with configurabledistribution of measurement points or resolution of pixels. The scanningpattern 1101 may be dynamically adjusted by generating a drive signal tothe scanning mirror. The drive signal may comprise multiple signalcomponents with a first component having a resonant frequency of thefast scan for producing a movement about the fast scan axis, a secondcomponent having a (resonant) frequency of the slow scan for producing amovement about the slow scan axis, a third component having a frequencytwice that of the fast scan frequency for producing a high frequencymovement about the slow scan axis (to correct raster pinch distortion),and a fourth component having a frequency and/or waveform for varyingthe speed of the slow scan motion (to adjust pixel density in selectedregions in the vertical direction).

The multiple components may be combined with a fixed phase difference orsynchronized with aid of a positional signal as described elsewhereherein. For example, the first component that has a resonant frequencyof the fast scan may be synchronized with the second component foractuating the low frequency motion of the slow scan with zero phasedifference (i.e., a horizontal sweep reaches its start/end when thevertical scan is at its start or end). This is also enabled by selectingthe resonant frequency and/or oscillation frequency for the oscillationmotions in the two directions such that one frequency is apre-determined times of the other one. Similarly, the first componentmay also be synchronized with the third component that has a frequencytwice of that of the first component for correcting the raster pinchdistortion. The fourth component and the second component may havecontrollable or configurable phase relationship or amplituderelationship such that the slow scan motion of the scanning mirror canbe controlled dynamically based on real-time conditions.

In some cases, pixel distribution along the horizontal direction or fastscanning direction may also be adjusted. This may be achieved bycontrolling the light sources for generating light pulses at desiredtime intervals. For example, in the case when fiber laser is utilized,the variable time intervals may be achieved by controlling the timeintervals of the seed light pulses.

In some situations, non-uniform pixels (points) distribution may bepreferred so that dense light spots may be emitted into a selectedregion in a controllable manner. For instance, light spots may bepreferred to be denser in the middle of the line scan or denser in aregion where target object is detected and details are desired. Thisbeneficially provides an adjustable resolution over a selected regionthereby improving the sampling and computation efficiency of Lidarimaging. As an example, pixel distribution and/or scanning pattern maybe adjusted dynamically in response to the detection of a potentialtarget. The scanning pattern or pixel distribution may be determineddynamically based on one or more real-time conditions including anenvironment condition or a condition of the Lidar system.

FIG. 12 schematically shows an example of configuring distribution anddensity of pixels/measurement points dynamically in response toreal-time conditions. In some cases, during a first operation setting1201, target of interest 1205 may be identified and more information forfurther identifying may be desired. In response to identifying thelocation of the target in the field of view, the provided system mayadopt a second operation setting 1203 and adjust the drive signalgenerated to the scanning mirror and the light sources accordingly. Thesecond operation setting may result in higher density of pixels ormeasurement points allocated to the region of the target of interest.

In some cases, the scanning pattern or pixel distribution may changedynamically to improve energy efficiency of the Lidar system. Forexample, when the Lidar system is detected to be in a less complexenvironment (e.g., rural place), a scanning pattern or resolution withfewer pixels allocated towards the edges of the field of view may beselected. This can be achieved by varying the drive signals or one ormore components of the drive signals for actuating the slow scan motionand/or adjusting the control signals for the light sources.

FIG. 13 schematically shows a block diagram of a control system 1300 fora scanner, in accordance with some embodiments of the invention. Thecontrol system 1300 can be the same as the scanner control unit asdescribed in FIG. 1. The scanning mirror 1301 may be controlled by thecontrol system 1300. The scanning mirror can be the same as the scanningmirror as described elsewhere herein. For example, the scanning mirrormay include a single multi-axis scanning mirror. In some embodiments,the scanning mirror 1303 may be actuated to rotate about a fast scanaxis and a slow scan axis.

The slow scan movement may be detected by a positional sensor. In somecases, the slow scan movement may be analyzed by a signal analyzer 1305.In some cases, the slow scan movement may be ramped vertical scan at afrequency twice that of the resonant frequency about the fast scan axis.The individual waveforms (characteristics of the oscillation motion)associated with the slow scan motion may be extracted by the signalanalyzer and fed to the controller 1307 for further adjusting orgenerating control signals to the slow scan control unit.

In some cases, the controller 1307 may be in communication with a mastercontroller or an external control entity. For example, the controller1307 may receive instructions from a master controller to adjust thedrive signal in order to change the slow scan movement of the scanningmirror. For instance, when a target is detected, the controller 1307 mayreceive instructions containing information about the location(coordinates) about the target. In response to the instruction, thecontroller 1307 may generate instructions to the slow scan waveformgenerator 1311 to generate a waveform or a component waveform of thedrive signal for varying the vertical/slow scan motion of the scanningmirror. For instance, a high frequency component or an individual highfrequency waveform with varying amplitude may be generated and added tothe signal component for actuating the slow scan motion therebydecreasing the moving speed in the target location. The variable highfrequency waveform may be combined with the other components with aid ofa clock signal produced by the clock 1309.

The individual waveform associated with the slow scan movement may thenbe transmitted to the slow scan control unit 1313 for generating controlsignals. A drivel signal component for actuating the slow scan movementmay be generated and combined with the drive signal component foractuating the fast scan movement.

The fast scan movement of the scanning mirror 1301 may be monitored anddetected by a positional sensor as described above. The fast scanmovement may be utilized for generating clock signals for synchronizingthe slow scan movement and the fast scan movement as described elsewhereherein. In some embodiments, clock signals may be generated by the clock1309 and supplied to the slow scan waveform generator 1311 to triggercontrol signals for the slow scan motion. The clock signals can also beused to synchronize or combine various signal components of thecomposite drive signal for various purposes as described above.

The fast scan movement may be fed to a fast scan control unit 1303 asfeedback information for generating control signals. The fast scancontrol unit 1303 may dynamically adjust the control signal or generatedrive signal for actuating the fast scan movement based on the feedbackinformation.

In some cases, the combined drive signal including the output from thefast scan control unit 1303 and the slow scan control unit 1313 may betransmitted to the driver circuit of the scanning mirror.

The control unit, functions, algorithms, operations, circuits or themethods may be implemented using software, hardware or firmware or acombination thereof. In some embodiments, the control unit may compriseone or more processors and at least one memory for storing programinstructions. The processors may be a component of the Lidar system.Alternatively, the processors may be external to the Lidar system but incommunication with the Lidar system. The processor(s) can be a single ormultiple microprocessors, field programmable gate arrays (FPGAs), ordigital signal processors (DSPs) capable of executing particular sets ofinstructions. Computer-readable instructions can be stored on a tangiblenon-transitory computer-readable medium, such as a flexible disk, a harddisk, a CD-ROM (compact disk-read only memory), and MO(magneto-optical), a DVD-ROM (digital versatile disk-read only memory),a DVD RAM (digital versatile disk-random access memory), or asemiconductor memory. The control unit may be a standalone device orsystem that is in communication with the Lidar system. Alternatively,the control unit may be a component of the Lidar system. The methodsdisclosed herein such as generating variable vertical scan motion inresponse to real-time condition can be implemented in hardwarecomponents or combinations of hardware and software such as, forexample, ASICs, special purpose computers, or general purpose computers.

The provided laser control or stabilization method and mechanism can beutilized in conjunction with various Lidar systems or can be used invarious applications. For example, when denser light spots are desiredin a given region the vertical scan motion may be varied. In such case,the aforementioned methods and mechanism may also provide stabilizationand raster pinch correction for the scanner.

A Lidar system equipped with the described scanner control mechanism maybe provided on a movable object to sense an environment surrounding themovable object. Alternatively, the Lidar system may be installed on astationary object.

A movable object of the present invention can be configured to movewithin any suitable environment, such as in air (e.g., a fixed-wingaircraft, a rotary-wing aircraft, or an aircraft having neither fixedwings nor rotary wings), in water (e.g., a ship or a submarine), onground (e.g., a motor vehicle, such as a car, truck, bus, van,motorcycle, bicycle; a movable structure or frame such as a stick,fishing pole; or a train), under the ground (e.g., a subway), in space(e.g., a spaceplane, a satellite, or a probe), or any combination ofthese environments. The movable object can be a vehicle, such as avehicle described elsewhere herein. In some embodiments, the movableobject can be carried by a living subject, or take off from a livingsubject, such as a human or an animal.

In some cases, the movable object can be an autonomous vehicle which maybe referred to as an autonomous car, driverless car, self-driving car,robotic car, or unmanned vehicle. In some cases, an autonomous vehiclemay refer to a vehicle configured to sense its environment and navigateor drive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In some instances, the Lidar systems may be integrated into a vehicle aspart of an autonomous-vehicle driving system. For example, a Lidarsystem may provide information about the surrounding environment to adriving system of an autonomous vehicle. In an example, the Lidar systemmay provide a 360 degree horizontal field of view of the vehicle. Anautonomous-vehicle driving system may include one or more computingsystems that receive information from a Lidar system about thesurrounding environment, analyze the received information, and providecontrol signals to the vehicle's driving systems (e.g., steering wheel,accelerator, brake, or turn signal).

As used herein A and/or B encompasses one or more of A or B, andcombinations thereof such as A and B. It will be understood thatalthough the terms “first,” “second,” “third” etc. are used herein todescribe various elements, components, regions and/or sections, theseelements, components, regions and/or sections should not be limited bythese terms. These terms are merely used to distinguish one element,component, region or section from another element, component, region orsection. Thus, a first element, component, region or section discussedherein could be termed a second element, component, region or sectionwithout departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including,” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components and/or groupsthereof.

Reference throughout this specification to “some embodiments,” or “anembodiment,” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrase “in someembodiment,” or “in an embodiment,” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. Numerous differentcombinations of embodiments described herein are possible, and suchcombinations are considered part of the present disclosure. In addition,all features discussed in connection with any one embodiment herein canbe readily adapted for use in other embodiments herein. It is intendedthat the following claims define the scope of the invention and thatmethods and structures within the scope of these claims and theirequivalents be covered thereby.

What is claimed is:
 1. A method for controlling a scanner of a Lidarsystem, comprising: producing a trigger signal by a positional sensor ofthe scanner; generating a single drive signal comprising a firstcomponent at a first frequency and a second component at a secondfrequency, wherein the first component and the second component aresuperposed with a fixed phase relationship with aid of the triggersignal; transmitting the single drive signal to the scanner, wherein thescanner has resonant responses at the first frequency; and actuating thescanner to move in a first periodic motion at the first frequency abouta first axis, and move in a second periodic motion at the secondfrequency about a second axis.
 2. The method of claim 1, wherein thescanner includes a single multi-axis mirror.
 3. The method of claim 1,wherein the first periodic motion is at a first resonant frequency ofthe scanner about the first axis and the second periodic motion is at asecond resonant frequency of the scanner about the second axis.
 4. Themethod of claim 1, wherein the second component comprises a rampwaveform.
 5. The method of claim 4, wherein the second componentcomprises a low frequency waveform component and a high frequencywaveform component.
 6. The method of claim 5, wherein the high frequencywaveform component is at a frequency twice that of the first frequencyof the first component.
 7. The method of claim 6, wherein the highfrequency waveform component and the low frequency waveform componentare synchronized with aid of the trigger signal.
 8. The method of claim5, wherein the high frequency waveform component has variable amplitude.9. The method of claim 8, wherein the high frequency waveform componentand the low frequency waveform component are combined with apre-determined phase relationship.
 10. The method of claim 8, whereinthe high frequency waveform component is generated in response toreal-time conditions.
 11. The method of claim 10, wherein the real-timeconditions include detection of a target.
 12. The method of claim 1,wherein the trigger signal is generated at the start or end of a sweepcycle of the first periodic motion.
 13. The method of claim 1, whereinthe second component is generated in response to receiving the triggersignal.
 14. The method of claim 1, wherein the scanner is directing asequence of light pulses along a scanning pattern that approximates araster scan pattern.
 15. The method of claim 14, further comprisingdynamically adjusting the scanning pattern along the second axisdirection according to real-time conditions.
 16. The method of claim 15,wherein adjusting the scanning pattern along the second axis directioncomprises varying the second periodic motion by superposing a highfrequency waveform component to the single drive signal.
 17. The methodof claim 16, wherein an amplitude or frequency of the high frequencywaveform component is determined based on the real-time conditions. 18.The method of claim 15, further comprising dynamically adjusting thescanning pattern along the first axis direction according to real-timeconditions.
 19. The method of claim 18, wherein adjusting the scanningpattern along the first axis direction comprises varying time intervalsof emitting the sequence of light pulses.
 20. A scanner for a Lidarsystem comprising: a scanner actuated to move in a first periodic motionat a first frequency about a first axis, and move in a second periodicmotion at a second frequency about a second axis; a positional sensorconfigured to generate a trigger signal; and a controller configured togenerate a single drive signal to actuate the scanner, wherein thesingle drive signal comprises a first component at the first frequencyand a second component at the second frequency, wherein the firstcomponent and the second component are superposed with a fixed phaserelationship with aid of the trigger signal.
 21. The scanner of claim20, wherein the scanner comprises a single multi-axis mirror.
 22. Thescanner of claim 21, wherein the single multi-axis mirror comprises ascan plate suspended from a gimbal via one or more torsion arms.
 23. Thescanner of claim 22, wherein the one or more torsion arms are in an Hshape.
 24. The scanner of claim 20, wherein the first periodic motion isat a first resonant frequency of the scanner about the first axis andthe second periodic motion is at a second resonant frequency of thescanner about the second axis.
 25. The scanner of claim 20, wherein thesecond component comprises a ramp waveform.
 26. The scanner of claim 25,wherein the second component comprises a low frequency waveformcomponent and a high frequency waveform component.
 27. The scanner ofclaim 26, wherein the high frequency waveform component is at afrequency twice that of the first frequency of the first component. 28.The scanner of claim 27, wherein the high frequency waveform componentand the low frequency waveform component are synchronized with aid ofthe trigger signal.
 29. The scanner of claim 20, wherein the triggersignal is generated at the start or end of a sweep cycle of the firstperiodic motion.
 30. The scanner of claim 20, wherein the controller isconfigured to generate the second component in response to receiving thetrigger signal.